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Character set division into "digits"

    Date: 22 September 1980 1525-EDT (Monday)
    From: Guy.Steele at CMU-10A
    To: bug-lisp at MIT-MC
    Subject:  DIGITP
    Message-Id: <22Sep80 152518 GS70@CMU-10A>
    .  .  .
    [I have been considering changing CHPROP so that DIGITP would take
    an optional argument (default 10.) specifying the radix.  Are there
    any objections to this
I've argued for a reader-independent notion of DIGITP, returning the digit's 
"weight" as you suggest, so that a *character set* standard can be proffered. 
Whether or not that predicate for "digitability" is called DIGITP is not much 
concern to me, but I would like to point out that that has been the definition 
in NIL;NEWFUN >  for almost two years;  furthermore, I'd sure hate to see that 
two-line, reader-useful function
    (DEFMACRO BASE-DIGITP (D &optional (B 10.) &aux (VAL (GENSYM))) 
       `(LET ((,VAL (DIGITP ,D)))
             (AND ,VAL (< ,VAL ,B) ,VAL)
fully displace the current DIGITP and thus wipe out all semblance of 
program-independence in the character standard.